Semiconductor device having air gap between gate electrode and source/drain pattern

ABSTRACT

A semiconductor device includes an active pattern on a substrate, a source/drain pattern on the active pattern, a channel pattern connected to the source/drain pattern, the channel pattern including semiconductor patterns stacked and spaced apart from each other, a gate electrode extending across the channel pattern, and inner spacers between the gate electrode and the source/drain pattern. The semiconductor patterns include stacked first and second semiconductor patterns. The gate electrode includes first and second portions, which are sequentially stacked between the substrate and the first and second semiconductor patterns, respectively. The inner spacers include first and second air gaps, between the first and second portions of the gate electrode and the source/drain pattern. The largest width of the first air gap is larger than that of the second air gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit under 35U.S.C. § 120 to, U.S. Application No. 17/242,823, filed on Apr. 28,2021, which claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2020-0112608, filed on Sep. 3, 2020, in the KoreanIntellectual Property Office, the entire contents of which are herebyincorporated by reference.

BACKGROUND

The present disclosure relates to a semiconductor device, and inparticular, to a semiconductor device including a field effecttransistor.

A semiconductor device may include an integrated circuit includingmetal-oxide-semiconductor field-effect transistors (MOS-FETs). To meetan increasing demand for a semiconductor device with a small patternsize and/or a reduced design rule, MOS-FETs may be scaled down. Thescale-down of the MOS-FETs may lead to deterioration in operationalproperties of the semiconductor device. A variety of studies are beingconducted to overcome technical limitations associated with thescale-down of the semiconductor device and/or to realize higherperformance semiconductor devices.

SUMMARY

Example embodiments of the inventive concepts provide a semiconductordevice with improved electric characteristics.

According to example embodiments of the inventive concepts, asemiconductor device may include an active pattern on a substrate, asource/drain pattern on the active pattern, a channel pattern connectedto the source/drain pattern, the channel pattern including semiconductorpatterns, stacked and spaced apart from each other, a gate electrodeextending across the channel pattern, and inner spacers between the gateelectrode and the source/drain pattern. The semiconductor patterns mayinclude a first semiconductor pattern at its lowermost level and asecond semiconductor pattern on the first semiconductor pattern. Thegate electrode may include a first portion between the substrate and thefirst semiconductor pattern and a second portion between the firstsemiconductor pattern and the second semiconductor pattern. The innerspacers may include a first air gap between the first portion of thegate electrode and the source/drain pattern and a second air gap betweenthe second portion of the gate electrode and the source/drain pattern.The largest width of the first air gap may be larger than the largestwidth of the second air gap.

According to example embodiments of the inventive concepts, asemiconductor device may include an active pattern on a substrate, asource/drain pattern on the active pattern, a channel pattern connectedto the source/drain pattern, the channel pattern including semiconductorpatterns, stacked and spaced apart from each other, a gate electrodeextending across the channel pattern, the gate electrode including aportion between the substrate and a lowermost one of the semiconductorpatterns, and an inner spacer between the portion of the gate electrodeand the source/drain pattern. The inner spacer may include an innerinsulating pattern and an air gap, defined by the inner insulatingpattern and the source/drain pattern. A width of the air gap mayincrease in a direction perpendicular to a top surface of the substrateuntil the width reaches its largest value and then the width maydecrease.

According to example embodiments of the inventive concepts, asemiconductor device may include a substrate including a PMOSFET regionand an NMOSFET region, adjacent to each other in a first direction, afirst active pattern and a second active pattern on the PMOSFET andNMOSFET regions, respectively, a first source/drain pattern and a secondsource/drain pattern on the first active pattern and the second activepattern, respectively, a first channel pattern and a second channelpattern, connected to the first source/drain pattern and the secondsource/drain pattern, respectively, and each of which includes a firstsemiconductor pattern, a second semiconductor pattern, and a thirdsemiconductor pattern that are sequentially stacked to be spaced apartfrom each other, a first gate electrode and a second gate electrode,crossing the first and second channel patterns, respectively, andextending in the first direction, each of the first and second gateelectrodes including a first portion between the substrate and the firstsemiconductor pattern, a second portion between the first semiconductorpattern and the second semiconductor pattern, a third portion betweenthe second semiconductor pattern and the third semiconductor pattern,and a fourth portion on the third semiconductor pattern, inner spacers,between the first to third portions of the second gate electrode and thesecond source/drain pattern, a first gate insulating layer and a secondgate insulating layer, between the first channel pattern and the firstgate electrode and between the second channel pattern and the secondgate electrode, respectively, a first gate spacer and a second gatespacer on side surfaces of the first and second gate electrodes,respectively, a first gate capping pattern and a second gate cappingpattern on top surfaces of the first and second gate electrodes,respectively, a first interlayer insulating layer on the first andsecond gate capping patterns, active contacts penetrating the firstinterlayer insulating layer and coupled to the first and secondsource/drain patterns, respectively, gate contacts penetrating the firstinterlayer insulating layer and coupled to the first and second gateelectrodes, respectively, a second interlayer insulating layer on thefirst interlayer insulating layer, a first metal layer in the secondinterlayer insulating layer, the first metal layer including firstinterconnection lines, connected to the active contacts and the gatecontacts, a third interlayer insulating layer on the second interlayerinsulating layer, and a second metal layer in the third interlayerinsulating layer. The second metal layer may include secondinterconnection lines, electrically connected to the firstinterconnection lines. Each of the inner spacers may include an innerinsulating pattern and an air gap, defined by the inner insulatingpattern and the second source/drain pattern. At least one of the firstto third portions of the second gate electrode may have a recessed sidesurface. The inner insulating pattern may include a firsthorizontally-extended portion at its top level, a secondhorizontally-extended portion at its bottom level, and a protrudingportion connecting the first and second horizontally-extended portionsto each other. The protruding portion may face the recessed side surfaceand may have a profile corresponding to the recessed side surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingbrief description taken in conjunction with the accompanying drawings.The accompanying drawings represent non-limiting, example embodiments asdescribed herein.

FIG. 1 is a plan view illustrating a semiconductor device according toexample embodiments of the inventive concepts.

FIGS. 2A to 2D are sectional views, which are respectively taken alonglines A-A′, B-B′, C-C′, and D-D′ of FIG. 1 .

FIG. 3 is an enlarged sectional view illustrating a portion M of FIG.2B.

FIGS. 4A to 10D are sectional views illustrating a method of fabricatinga semiconductor device according to example embodiments of the inventiveconcepts.

FIGS. 11 to 19 are enlarged sectional views, which are provided toillustrate a method of forming an inner spacer according to exampleembodiments of the inventive concepts and to illustrate a portion M ofFIGS. 6B and 7B.

FIGS. 20 to 22 are enlarged sectional views, each of which is providedto described a semiconductor device according to example embodiments ofthe inventive concepts and to illustrate the portion M of FIG. 2B.

FIG. 23 is a sectional view, which is taken along the line A-A′ of FIG.1 to illustrate a semiconductor device according to example embodimentsof the inventive concepts.

DETAILED DESCRIPTION

FIG. 1 is a plan view illustrating a semiconductor device according toexample embodiments of the inventive concepts. FIGS. 2A to 2D aresectional views, which are respectively taken along lines A-A′, B-B′,C-C′, and D-D′ of FIG. 1 . FIG. 3 is an enlarged sectional viewillustrating a portion M of FIG. 2B.

Referring to FIGS. 1 and 2A to 2D, a logic cell LC may be provided on asubstrate 100. Logic transistors constituting a logic circuit may bedisposed on the logic cell LC. The substrate 100 may be a semiconductorsubstrate, which is formed of or includes silicon, germanium,silicon-germanium, or the like, or a compound semiconductor substrate.As an example, the substrate 100 may be a silicon wafer.

The logic cell LC may include a PMOSFET region PR and an NMOSFET regionNR. The PMOSFET and NMOSFET regions PR and NR may be defined by a secondtrench TR2, which is formed in an upper portion of the substrate 100. Inother words, the second trench TR2 may be placed between the PMOSFET andNMOSFET regions PR and NR. The PMOSFET and NMOSFET regions PR and NR maybe spaced apart from each other, in a first direction D1, with thesecond trench TR2 interposed therebetween.

A first active pattern AP1 and a second active pattern AP2 may bedefined by a first trench TR1, which is formed in an upper portion ofthe substrate 100. The first and second active patterns AP1 and AP2 maybe provided on the PMOSFET and NMOSFET regions PR and NR, respectively.The first trench TR1 may be shallower than the second trench TR2. Thefirst and second active patterns AP1 and AP2 may be extended in a seconddirection D2. The first and second active patterns AP1 and AP2 may bevertically-protruding portions of the substrate 100.

A device isolation layer ST may be provided to fill the first and secondtrenches TR1 and TR2. The device isolation layer ST may include asilicon oxide layer. Upper portions of the first and second activepatterns AP1 and AP2 may protrude vertically above the device isolationlayer ST (e.g., see FIG. 2D). The device isolation layer ST may notcover the upper portions of the first and second active patterns AP1 andAP2. The device isolation layer ST may cover lower side surfaces of thefirst and second active patterns AP1 and AP2.

The first active pattern AP1 may include an upper portion serving as afirst channel pattern CH1. The second active pattern AP2 may include anupper portion serving as a second channel pattern CH2. Each of the firstand second channel patterns CH1 and CH2 may include a firstsemiconductor pattern SP1, a second semiconductor pattern SP2, and athird semiconductor pattern SP3, which are sequentially stacked. Thefirst to third semiconductor patterns SP1, SP2, and SP3 may be spacedapart from each other in a vertical direction (e.g., a third directionD3).

Each of the first to third semiconductor patterns SP1, SP2, and SP3 maybe formed of or include silicon (Si), germanium (Ge), orsilicon-germanium (SiGe). In example embodiments, each of the first tothird semiconductor patterns SP1, SP2, and SP3 may be formed of orinclude crystalline silicon.

A plurality of first recesses RS1 may be formed in the upper portion ofthe first active pattern AP1. First source/drain patterns SD1 may beprovided in the first recesses RS1, respectively. The first source/drainpatterns SD1 may be impurity regions of a first conductivity type (e.g.,p-type). The first channel pattern CH1 may be interposed between eachpair of the first source/drain patterns SD1. In other words, each pairof the first source/drain patterns SD1 may be connected to each other bythe stacked first to third semiconductor patterns SP1, SP2, and SP3 ofthe first channel pattern CH1.

A plurality of second recesses RS2 may be formed in the upper portion ofthe second active pattern AP2. Second source/drain patterns SD2 may beprovided in the second recesses RS2, respectively. The secondsource/drain patterns SD2 may be impurity regions of a secondconductivity type (e.g., n-type). The second channel pattern CH2 may beinterposed between each pair of the second source/drain patterns SD2. Inother words, each pair of the second source/drain patterns SD2 may beconnected to each other by the stacked first to third semiconductorpatterns SP1, SP2, and SP3 of the second channel pattern CH2.

The first and second source/drain patterns SD1 and SD2 may be epitaxialpatterns, which are formed by a selective epitaxial growth (SEG)process. As an example, each of the first and second source/drainpatterns SD1 and SD2 may have a top surface that is located at the sameor substantially the same level as a top surface of the thirdsemiconductor pattern SP3. However, in example embodiments, the topsurface of each of the first and second source/drain patterns SD1 andSD2 may be higher than the top surface of the third semiconductorpattern SP3.

The first source/drain patterns SD1 may include a semiconductor material(e.g., SiGe) having a lattice constant greater than that of thesubstrate 100. In some example embodiments, the pair of the firstsource/drain patterns SD1 may exert a compressive stress on the firstchannel patterns CH1 therebetween. The second source/drain patterns SD2may be formed of or include the same semiconductor material (e.g., Si)as the substrate 100.

Each of the first source/drain patterns SD1 may include a firstsemiconductor layer SEL1 and a second semiconductor layer SEL2, whichare sequentially stacked. A sectional shape of the first source/drainpattern SD1 taken parallel to the second direction D2 will be describedwith reference to FIG. 2A.

The first semiconductor layer SEL1 may cover an inner surface of a firstrecess RS1. The first semiconductor layer SEL1 may have a decreasingthickness in an upward direction. For example, the thickness of thefirst semiconductor layer SEL1, which is measured in the third directionD3 at the bottom level of the first recess RS1, may be larger than thethickness of the first semiconductor layer SEL1, which is measured inthe second direction D2 at the top level of the first recess RS1. Thefirst semiconductor layer SEL1 may have a ‘U’-shaped section, due to asectional profile of the first recess RS1.

The second semiconductor layer SEL2 may fill a remaining space of thefirst recess RS1 excluding the first semiconductor layer SEL1. A volumeof the second semiconductor layer SEL2 may be larger than a volume ofthe first semiconductor layer SEL1. In other words, a ratio of a volumeof the second semiconductor layer SEL2 to a total volume of the firstsource/drain pattern SD1 may be greater than a ratio of a volume of thefirst semiconductor layer SEL1 to the total volume of the firstsource/drain pattern SD1.

Each of the first and second semiconductor layers SEL1 and SEL2 may beformed of or include silicon-germanium (SiGe). In detail, the firstsemiconductor layer SEL1 may be provided to have a relatively lowgermanium concentration. In other example embodiments, the firstsemiconductor layer SEL1 may be provided to contain only silicon (Si)and not germanium (Ge). The germanium concentration of the firstsemiconductor layer SEL1 may range from 0 at% to 10 at%.

The second semiconductor layer SEL2 may be provided to have a relativelyhigh germanium concentration. As an example, the germanium concentrationof the second semiconductor layer SEL2 may range from 30 at% to 70 at%.The germanium concentration of the second semiconductor layer SEL2 mayincrease in the third direction D3. For example, the germaniumconcentration of the second semiconductor layer SEL2 may be about 40 at%near the first semiconductor layer SEL1 but may be about 60 at% at itstop level.

The first and second semiconductor layers SEL1 and SEL2 may includeimpurities (e.g., boron), allowing the first source/drain pattern SD1 tohave the p-type conductivity. In example embodiments, a concentration ofimpurities in the second semiconductor layer SEL2 (in at%) may begreater than that in the first semiconductor layer SEL1.

The first semiconductor layer SEL1 may reduce or prevent a stackingfault from occurring between the substrate 100 and the secondsemiconductor layer SEL2 and between the first to third semiconductorpatterns SP1, SP2, and SP3 and the second semiconductor layer SEL2. Thestacking fault may lead to an increase of a channel resistance. Thestacking fault may easily occur on the bottom of the first recess RS1.Thus, if the first semiconductor layer SEL1 adjacent to the first recessRS1 is provided to have a relatively large thickness, the stacking faultmay be reduced or prevented.

The first semiconductor layer SEL1 may protect the second semiconductorlayer SEL2, in a process of replacing sacrificial layers SAL with firstto third portions PO1, PO2, and PO3 of a gate electrode GE. For example,the first semiconductor layer SEL1 may reduce or prevent the secondsemiconductor layer SEL2 from being undesirably etched by an etchingmaterial, which is used to remove the sacrificial layers SAL.

The gate electrodes GE may be provided to cross the first and secondactive patterns AP1 and AP2 and to extend in the first direction D1. Thegate electrodes GE may be arranged with a first pitch P1 in the seconddirection D2. Each of the gate electrodes GE may be overlapped with thefirst and second channel patterns CH1 and CH2 when viewed in a planview.

The gate electrode GE may include a first portion PO1 interposed betweenthe substrate 100 and the first semiconductor pattern SP1, a secondportion PO2 interposed between the first semiconductor pattern SP1 andthe second semiconductor pattern SP2, a third portion PO3 interposedbetween the second semiconductor pattern SP2 and the third semiconductorpattern SP3, and a fourth portion PO4 on the third semiconductor patternSP3.

Referring back to FIG. 2A, the first to third portions PO1, PO2, and PO3of the gate electrode GE on the PMOSFET region PR may have differentwidths from each other. For example, the largest width of the thirdportion PO3 in the second direction D2 may be larger than the largestwidth of the second portion PO2 in the second direction D2. The largestwidth of the first portion PO1 in the second direction D2 may be largerthan the largest width of the third portion PO3 in the second directionD2.

Referring back to FIG. 2D, the gate electrode GE may be provided on atop surface TS, a bottom surface BS, and opposite side surfaces SW ofeach of the first to third semiconductor patterns SP1, SP2, and SP3. Inother words, the logic transistor according to the present exampleembodiments may be a three-dimensional field-effect transistor (e.g.,multi-bridge channel field-effect transistor (MBCFET)), in which thegate electrode GE is provided to three-dimensionally surround thechannel pattern.

Referring back to FIGS. 1 and 2A to 2D, a pair of gate spacers GS may berespectively disposed on opposite side surfaces of the fourth portionPO4 of the gate electrode GE. The gate spacers GS may be extended alongthe gate electrode GE and in the first direction D1. Top surfaces of thegate spacers GS may be higher than a top surface of the gate electrodeGE. The top surfaces of the gate spacers GS may be coplanar with a topsurface of a first interlayer insulating layer 110, which will bedescribed below. The gate spacers GS may be formed of or include atleast one of SiCN, SiCON, or SiN. In example embodiments, the gatespacers GS may have a multi-layered structure including at least twolayers, each of which is made of SiCN, SiCON, or SiN.

A gate capping pattern GP may be provided on the gate electrode GE. Thegate capping pattern GP may be extended along the gate electrode GE andin the first direction D1. The gate capping pattern GP may be formed ofor include a material having an etch selectivity with respect to firstand second interlayer insulating layers 110 and 120, which will bedescribed below. For example, the gate capping patterns GP may be formedof or include at least one of SiON, SiCN, SiCON, or SiN.

A gate insulating layer GI may be interposed between the gate electrodeGE and the first channel pattern CH1 and between the gate electrode GEand the second channel pattern CH2. The gate insulating layer GI maycover the top surface TS, the bottom surface BS, and the opposite sidesurfaces SW of each of the first to third semiconductor patterns SP1,SP2, and SP3. The gate insulating layer GI may cover the top surface ofthe device isolation layer ST below the gate electrode GE (e.g., seeFIG. 2D).

In example embodiments, the gate insulating layer GI may include asilicon oxide layer, a silicon oxynitride layer, and/or a high-kdielectric layer. The high-k dielectric layer may be formed of orinclude at least one of high-k dielectric materials whose dielectricconstants are higher than that of silicon oxide. As an example, thehigh-k dielectric materials may be formed of or include at least one ofhafnium oxide, hafnium silicon oxide, hafnium zirconium oxide, hafniumtantalum oxide, lanthanum oxide, zirconium oxide, zirconium siliconoxide, tantalum oxide, titanium oxide, barium strontium titanium oxide,barium titanium oxide, strontium titanium oxide, lithium oxide, aluminumoxide, lead scandium tantalum oxide, and/or lead zinc niobate.

In other example embodiments, the semiconductor device may include anegative capacitance (NC) FET using a negative capacitor. For example,the gate insulating layer GI may include a ferroelectric layerexhibiting a ferroelectric material property and a paraelectric layerexhibiting a paraelectric material property.

The ferroelectric layer may have a negative capacitance, and theparaelectric layer may have a positive capacitance. In exampleembodiments where two or more capacitors are connected in series andeach capacitor has a positive capacitance, a total capacitance may beless than a capacitance of each of the capacitors. By contrast, inexample embodiments where at least one of serially-connected capacitorshas a negative capacitance, a total capacitance of theserially-connected capacitors may have a positive value and may begreater than an absolute value of each capacitance.

In example embodiments where a ferroelectric layer having a negativecapacitance and a paraelectric layer having a positive capacitance areconnected in series, a total capacitance of the serially-connectedferroelectric and paraelectric layers may be increased. Due to such anincrease of the total capacitance, a transistor including theferroelectric layer may have a subthreshold swing (SS) less than 60mV/decade, at the room temperature.

The ferroelectric layer may have a ferroelectric material property. Theferroelectric layer may be formed of or include at least one of, forexample, hafnium oxide, hafnium zirconium oxide, barium strontiumtitanium oxide, barium titanium oxide, and/or lead zirconium titaniumoxide. Here, the hafnium zirconium oxide may be hafnium oxide that isdoped with zirconium (Zr). Alternatively, the hafnium zirconium oxidemay be a compound composed of hafnium (Hf), zirconium (Zr), and/oroxygen (O).

The ferroelectric layer may further include dopants. For example, thedopants may include at least one of aluminum (Al), titanium (Ti),niobium (Nb), lanthanum (La), yttrium (Y), magnesium (Mg), silicon (Si),calcium (Ca), cerium (Ce), dysprosium (Dy), erbium (Er), gadolinium(Gd), germanium (Ge), scandium (Sc), strontium (Sr), and/or tin (Sn).The kind of the dopants in the ferroelectric layer may vary depending ona ferroelectric material included in the ferroelectric layer.

In example embodiments where the ferroelectric layer includes hafniumoxide, the dopants in the ferroelectric layer may include at least oneof, for example, gadolinium (Gd), silicon (Si), zirconium (Zr), aluminum(Al), and/or yttrium (Y).

In example embodiments where the dopants are aluminum (Al), a content ofaluminum in the ferroelectric layer may range from 3 to 8 at% (atomicpercentage). Here, the content of the aluminum as the dopants may be aratio of the number of aluminum atoms to the number of hafnium andaluminum atoms.

In example embodiments where the dopants are silicon (Si), a content ofsilicon in the ferroelectric layer may range from 2 at% to 10 at%. Inexample embodiments where the dopants are yttrium (Y), a content ofyttrium in the ferroelectric layer may range from 2 at% to 10 at%. Inexample embodiments where the dopants are gadolinium (Gd), a content ofgadolinium in the ferroelectric layer may range from 1 at% to 7 at%. Inexample embodiments where the dopants are zirconium (Zr), a content ofzirconium in the ferroelectric layer may range from 50 at% to 80 at%.

The paraelectric layer may have a paraelectric material property. Theparaelectric layer may be formed of or include at least one of, forexample, silicon oxide and/or high-k metal oxides. The metal oxides,which can be used as the paraelectric layer, may include at least oneof, for example, hafnium oxide, zirconium oxide, and/or aluminum oxide,but the inventive concepts are not limited to these examples.

The ferroelectric layer and the paraelectric layer may be formed of orinclude the same material. The ferroelectric layer may have theferroelectric material property, but the paraelectric layer may not havethe ferroelectric material property. For example, in example embodimentswhere the ferroelectric and paraelectric layers contain hafnium oxide, acrystal structure of the hafnium oxide in the ferroelectric layer may bedifferent from a crystal structure of the hafnium oxide in theparaelectric layer.

The ferroelectric layer may exhibit the ferroelectric material property,only when it is in a specific range of thickness. In exampleembodiments, the ferroelectric layer may have a thickness ranging from0.5 to 10 nm, but the inventive concepts are not limited to thisexample. Since a critical thickness associated with the occurrence ofthe ferroelectric material property varies depending on the kind of theferroelectric material, the thickness of the ferroelectric layer may bechanged depending on the kind of the ferroelectric material.

As an example, the gate insulating layer GI may include a singleferroelectric layer. As another example, the gate insulating layer GImay include a plurality of ferroelectric layers spaced apart from eachother. The gate insulating layer GI may have a multi-layered structure,in which a plurality of ferroelectric layers and a plurality ofparaelectric layers are alternately stacked.

The gate electrode GE may include a first metal pattern and a secondmetal pattern on the first metal pattern. The first metal pattern may beprovided on the gate insulating layer GI and may be adjacent to thefirst to third semiconductor patterns SP1, SP2, and SP3. The first metalpattern may include a work function metal, which can be used to adjust athreshold voltage of the transistor. By adjusting a thickness andcomposition of the first metal pattern, it may be possible to realize atransistor having a desired threshold voltage. For example, the first tothird portions PO1, PO2, and PO3 of the gate electrode GE may becomposed of the first metal pattern or the work function metal.

The first metal pattern may include a metal nitride layer. For example,the first metal pattern may include at least one metal, which isselected from the group consisting of titanium (Ti), tantalum (Ta),aluminum (Al), tungsten (W) and molybdenum (Mo), and nitrogen (N). Inexample embodiments, the first metal pattern may further include carbon(C). The first metal pattern may include a plurality of work functionmetal layers, which are stacked.

The second metal pattern may include a metallic material whoseresistance is lower than the first metal pattern. For example, thesecond metal pattern may include at least one metal selected from thegroup consisting of tungsten (W), aluminum (Al), titanium (Ti), andtantalum (Ta). For example, the fourth portion PO4 of the gate electrodeGE may include the first metal pattern and the second metal pattern onthe first metal pattern.

Referring back to FIG. 2B, inner spacers IP may be provided on theNMOSFET region NR. Each of the inner spacers IP may be interposedbetween the second source/drain pattern SD2 and a corresponding one ofthe first to third portions PO1, PO2, and PO3 of the gate electrode GE.The inner spacers IP may be in direct contact with the secondsource/drain pattern SD2. Each of the first to third portions PO1, PO2,and PO3 of the gate electrode GE may be spaced apart from the secondsource/drain pattern SD2 by the inner spacer IP. The inner spacer IPwill be described in more detail with reference to FIG. 3 .

A first interlayer insulating layer 110 may be provided on the substrate100. The first interlayer insulating layer 110 may cover the gatespacers GS and the first and second source/drain patterns SD1 and SD2.The first interlayer insulating layer 110 may have a top surface that issubstantially coplanar with the top surface of the gate capping patternGP and the top surface of the gate spacer GS. A second interlayerinsulating layer 120 may be formed on the first interlayer insulatinglayer 110 to cover the gate capping pattern GP. In example embodiments,at least one of the first and second interlayer insulating layers 110and 120 may include a silicon oxide layer.

A pair of dividing structures DB, which are opposite to each other inthe second direction D2, may be provided at both sides of the logic cellLC. The dividing structure DB may be extended in the first direction D1and parallel to the gate electrodes GE. A pitch between the dividingstructure DB and the gate electrode GE adjacent to each other may beequal to the first pitch P1.

The dividing structure DB may be provided to penetrate the first andsecond interlayer insulating layers 110 and 120 and may be extended intothe first and second active patterns AP1 and AP2. The dividing structureDB may penetrate an upper portion of each of the first and second activepatterns AP1 and AP2. The dividing structure DB may separate the PMOSFETand NMOSFET regions PR and NR of the logic cell LC from an active regionof another logic cell adjacent thereto.

The upper portion of each of the first and second active patterns AP1and AP2 may further include sacrificial layers SAL adjacent to thedividing structure DB. The sacrificial layers SAL may be stacked to bespaced apart from each other. Each of the sacrificial layers SAL may belocated at the same level as a corresponding one of the first to thirdportions PO1, PO2, and PO3 of the gate electrode GE. The dividingstructure DB may be provided to penetrate the sacrificial layers SAL.

The sacrificial layers SAL may be formed of or include silicon-germanium(SiGe). A germanium concentration of each of the sacrificial layers SALmay range from 10 at% to 30 at%. The germanium concentration of thesacrificial layer SAL may be higher than the germanium concentration ofthe first semiconductor layer SEL1 described above.

Active contacts AC may be provided to penetrate the first and secondinterlayer insulating layers 110 and 120 and may be electricallyconnected to the first and second source/drain patterns SD1 and SD2,respectively. A pair of the active contacts AC may be respectivelyprovided at both sides of the gate electrode GE. When viewed in a planview, the active contact AC may have a bar shape elongated in the firstdirection D1.

The active contact AC may be a self-aligned contact. For example, theactive contact AC may be formed by a self-alignment process using thegate capping pattern GP and the gate spacer GS. In example embodiments,the active contact AC may cover at least a portion of a side surface ofthe gate spacer GS. Although not shown, the active contact AC may beprovided to cover a portion of the top surface of the gate cappingpattern GP.

Silicide patterns SC may be respectively interposed between the activecontact AC and the first source/drain pattern SD1 and between the activecontact AC and the second source/drain pattern SD2. The active contactAC may be electrically connected to the source/drain pattern SD1 or SD2through the silicide pattern SC. The silicide pattern SC may be formedof or include at least one of metal silicide materials (e.g., titaniumsilicide, tantalum silicide, tungsten silicide, nickel silicide, andcobalt silicide).

A gate contact GC, which is electrically connected to the gate electrodeGE, may be provided to penetrate the second interlayer insulating layer120 and the gate capping pattern GP. Referring to FIG. 2B, an upperregion of each of the active contacts AC adjacent to the gate contact GCmay be filled with an upper insulating pattern UIP. Accordingly, it maybe possible to reduce or prevent a process failure (e.g., a shortcircuit), which may occur when the gate contact GC is in contact withthe active contact AC adjacent thereto.

Each of the active and gate contacts AC and GC may include a conductivepattern FM and a barrier pattern BM enclosing the conductive pattern FM.For example, the conductive pattern FM may be formed of or include atleast one metal of aluminum, copper, tungsten, molybdenum, or cobalt.The barrier pattern BM may be provided to cover side and bottom surfacesof the conductive pattern FM. In example embodiments, the barrierpattern BM may include a metal layer and a metal nitride layer. Themetal layer may be formed of or include at least one of titanium,tantalum, tungsten, nickel, cobalt, or platinum. The metal nitride layermay include at least one of titanium nitride (TiN), tantalum nitride(TaN), tungsten nitride (WN), nickel nitride (NiN), cobalt nitride(CoN), or platinum nitride (PtN).

A first metal layer M1 may be provided in a third interlayer insulatinglayer 130. The first metal layer M1 may include first lowerinterconnection lines M1_R, second lower interconnection lines M1_I, andlower vias VI1. The lower vias VI1 may be provided below the first andsecond lower interconnection lines M1_R and M1_I.

Each of the first lower interconnection lines M1_R may be extended inthe second direction D2 to cross the logic cell LC. Each of the firstlower interconnection lines M1_R may be a power line. For example, adrain voltage VDD or a source voltage VSS may be applied to the firstlower interconnection line M1_R.

Referring to FIG. 1 , a first cell boundary CB1 extending in the seconddirection D2 may be defined in a region of the logic cell LC. A secondcell boundary CB2 extending in the second direction D2 may be defined ina region of the logic cell LC opposite to the first cell boundary CB1.The first lower interconnection line M1_R, to which the drain voltageVDD (e.g., a power voltage) is applied, may be disposed on the firstcell boundary CB1. The first lower interconnection line M1_R, to whichthe drain voltage VDD is applied, may be extended along the first cellboundary CB1 and in the second direction D2. The first lowerinterconnection line M1_R, to which the source voltage VSS (e.g., aground voltage) is applied, may be disposed on the second cell boundaryCB2. The first lower interconnection line M1_R, to which the sourcevoltage VSS is applied, may be extended along the second cell boundaryCB2 and in the second direction D2.

The second lower interconnection lines M1_I may be disposed between thefirst lower interconnection lines M1_R, to which the drain voltage VDDand the source voltage VSS are respectively applied, in the firstdirection D1. Each of the second lower interconnection lines M1_I may bea line- or bar-shaped pattern extending in the second direction D2. Thesecond lower interconnection lines M1_I may be arranged to be spacedapart from each other with a second pitch P2 in the first direction D1.The second pitch P2 may be smaller than the first pitch P1.

The lower vias VI1 may be provided below the first and second lowerinterconnection lines M1_R and M1_I of the first metal layer M1. Thelower vias VI1 may be respectively interposed between the activecontacts AC and the first and second lower interconnection lines M1_Rand M1_I. The lower vias VI1 may be respectively interposed between thegate contacts GC and the second lower interconnection lines M1_I.

The lower interconnection line M1_R or M1_I of the first metal layer M1and the lower via VI1 thereunder may be formed by separate processes. Inother words, each of the lower interconnection line M1_R or M1_I and thelower via VI1 may be a single damascene process. The semiconductordevice according to the present example embodiments may be fabricatedusing a sub-20 nm process.

A second metal layer M2 may be provided in a fourth interlayerinsulating layer 140. The second metal layer M2 may include upperinterconnection lines M2_I. Each of the upper interconnection lines M2_Imay be a line- or bar-shaped pattern extending in the first directionD1. In other words, the upper interconnection lines M2_I may be extendedin the first direction D1 to be parallel to each other. When viewed in aplan view, the upper interconnection lines M2_I may be parallel to thegate electrodes GE. The upper interconnection lines M2_I may be arrangedwith a third pitch P3 in the second direction D2. The third pitch P3 maybe smaller than the first pitch P1. The third pitch P3 may be largerthan the second pitch P2.

The second metal layer M2 may further include upper vias VI2. The uppervias VI2 may be provided below the upper interconnection lines M2_I. Theupper vias VI2 may be respectively interposed between the lowerinterconnection lines M1_R and M1_I and the upper interconnection linesM2_I.

The upper interconnection line M2_I of the second metal layer M2 and theupper via VI2 thereunder may be formed by the same process and may forma single object. In other words, the upper interconnection line M2_I ofthe second metal layer M2 and the upper via VI2 may be formed by a dualdamascene process.

The lower interconnection lines M1_R and M1_I of the first metal layerM1 and the upper interconnection lines M2_I of the second metal layer M2may be formed of or include the same material or different conductivematerials. For example, the lower interconnection lines M1_R and M1_Iand the upper interconnection lines M2_I may be formed of or include atleast one of metallic materials (e.g., aluminum, copper, tungsten,molybdenum, or cobalt).

In example embodiments, although not shown, additional metal layers(e.g., M3, M4, M5, and so forth) may be further stacked on the fourthinterlayer insulating layer 140. Each of the stacked metal layers mayinclude routing lines.

Now, the inner spacers IP on the NMOSFET region NR will be described inmore detail with reference to FIG. 3 . The inner spacers IP may berespectively interposed between the first to third portions PO1, PO2,and PO3 of the gate electrode GE and the second source/drain patternSD2. Each of the inner spacers IP may include an inner insulatingpattern ISP and an air gap AG.

Each of the first to third portions PO1, PO2, and PO3 of the gateelectrode GE may include a recessed side surface RSW. The recessed sidesurface RSW may be recessed in a direction away from the secondsource/drain pattern SD2. The inner insulating pattern ISP may beprovided to be adjacent to the recessed side surface RSW and may facethe recessed side surface RSW. The gate insulating layer GI may beinterposed between the inner insulating pattern ISP and the recessedside surface RSW.

The inner insulating pattern ISP may have the shape of letter ‘C’.Specifically, the inner insulating pattern ISP may include a firsthorizontally-extended portion HP1 and a second horizontally-extendedportion HP2, which are respectively provided at top and bottom levels ofthe inner spacer IP, and a protruding portion PRP, which is provided toconnect the first and second horizontally-extended portions HP1 and HP2to each other. Each of the first and second horizontally-extendedportions HP1 and HP2 may be extended in the second direction D2. Each ofthe first and second horizontally-extended portions HP1 and HP2 may bein direct contact with the semiconductor pattern SP1, SP2, or SP3.

As an example, the first and second horizontally-extended portions HP1and HP2 of the inner insulating pattern ISP may have different lengthsin the second direction D2. The second horizontally-extended portion HP2may be longer than the first horizontally-extended portion HP1.

The protruding portion PRP may be extended in the third direction D3 toconnect the first and second horizontally-extended portions HP1 and HP2to each other. The protruding portion PRP may be provided to face therecessed side surface RSW. The protruding portion PRP may have a profilecorresponding to the recessed side surface RSW. In other words, theprotruding portion PRP may protrude in a direction away from the secondsource/drain pattern SD2. The protruding portion PRP may protrude towardthe portion PO1, PO2, or PO3 of the gate electrode GE.

A side surface OSW of the second source/drain pattern SD2 may include afirst side surface OSW1 and a second side surface OSW2. The first sidesurface OSW1 may be in contact with the air gap AG, and the second sidesurface OSW2 may be in contact with the semiconductor pattern SP1, SP2,or SP3. A bottom surface OBS of the second source/drain pattern SD2 maybe in contact with a bottom of the second recess RS2 (e.g., thesubstrate 100).

The inner insulating pattern ISP may be formed of or include at leastone of low-k dielectric materials. The low-k dielectric materials mayinclude silicon oxide or dielectric materials whose dielectric constantsare lower than that of silicon oxide. For example, the low-k dielectricmaterials may include silicon oxide, fluorine- or carbon-doped siliconoxide, porous silicon oxide, or organic polymeric dielectric materials.

The air gap AG may be interposed between the inner insulating patternISP and the second source/drain pattern SD2. The air gap AG may beenclosed by the first and second horizontally-extended portions HP1 andHP2, the protruding portion PRP, and the first side surface OSW1. Theair gap AG may be an empty space, which is defined by the first andsecond horizontally-extended portions HP1 and HP2, the protrudingportion PRP, and the first side surface OSW1. The air gap AG may befilled with the air or a gaseous substance.

The air gap AG may include a first air gap AG1 between the substrate 100and the first semiconductor pattern SP1, a second air gap AG2 betweenthe first semiconductor pattern SP1 and the second semiconductor patternSP2, and a third air gap AG3 between the second semiconductor patternSP2 and the third semiconductor pattern SP3.

In example embodiments, a width of the first air gap AG1 in the seconddirection D2 may vary in the third direction D3. Specifically, the widthof the first air gap AG1 may be increased in the third direction D3until it reaches its largest value, and then may be decreased. The firstair gap AG1 may have a first width W1 at its bottom level, a secondwidth W2 at its intermediate level, and a third width W3 at its toplevel. The second width W2 may be larger than the first width W1, andthe first width W1 may be larger than the third width W3. That is, thewidth of the first air gap AG1 may have the largest width W2 at itsintermediate level.

The largest width of the second air gap AG2 may be a fourth width W4,and the largest width of the third air gap AG3 may be a fifth width W5.The largest widths of the first to third air gaps AG1, AG2, and AG3 maybe different from each other. For example, the largest width W2 of thefirst air gap AG1 may be larger than the largest width W4 of the secondair gap AG2, and the largest width W4 of the second air gap AG2 may belarger than the largest width W5 of the third air gap AG3. That is, thelargest widths of the first to third air gaps AG1, AG2, and AG3 may begradually decreased in the third direction D3.

According to the present example embodiments, the air gap AG may have avolume that is larger than that of the inner spacer IP. In other words,a volume fraction of the air gap AG in the inner spacer IP may begreater than a volume fraction of the inner insulating pattern ISP inthe inner spacer IP. Thus, a dielectric constant of the inner spacer IPmay be mainly determined by the air gap AG. As a result, the dielectricconstant of the inner spacer IP may be lowered to a value close to thedielectric constant of the air.

Due to the dielectric material (e.g., the inner spacer IP) interposedbetween the gate electrode GE and the second source/drain pattern SD2, aparasitic capacitor may be formed between the gate electrode GE and thesecond source/drain pattern SD2. The presence of the parasitic capacitormay lead to deterioration in performance and electric characteristics ofthe semiconductor device.

According to example embodiments of the inventive concepts, the innerspacer IP may have a very low dielectric constant, because it isprovided as a combination of the inner insulating pattern ISP, which isformed of a low-k dielectric material, and the air gap AG. Due to thelow dielectric constant of the inner spacer IP, the parasitic capacitorbetween the gate electrode GE and the second source/drain pattern SD2may have low capacitance. Accordingly, the semiconductor deviceaccording to example embodiments of the inventive concepts may beprovided to have improved performance and electric characteristics.

FIGS. 4A to 10D are sectional views illustrating a method of fabricatinga semiconductor device according to example embodiments of the inventiveconcepts. Specifically, FIGS. 4A, 5A, 6A, 7A, 8A, 9A, and 10A aresectional views corresponding to the line A-A′ of FIG. 1 . FIGS. 6B, 7B,8B, 9B, and 10B are sectional views corresponding to the line B-B′ ofFIG. 1 . FIGS. 6C, 7C, 8C, 9C, and 10C are sectional views correspondingto the line C-C′ of FIG. 1 . FIGS. 4B, 5B, 6D, 7D, 8D, 9D, and 10D aresectional views corresponding to the line D-D′ of FIG. 1 . FIGS. 11 to19 are sectional views illustrating a portion M of FIGS. 6B and 7B andillustrating a method of forming an inner spacer according to exampleembodiments of the inventive concepts.

Referring to FIGS. 4A and 4B, a substrate 100 including a PMOSFET regionPR and an NMOSFET region NR may be provided. Sacrificial layers SAL andactive layers ACL, which are alternately stacked on the substrate 100,may be formed. The sacrificial layers SAL may be formed of or include atleast one of silicon (Si), germanium (Ge), or silicon-germanium (SiGe),and the active layers ACL may be formed of or include at least one ofsilicon (Si), germanium (Ge), or silicon-germanium (SiGe).

For example, the sacrificial layers SAL may be formed of or includesilicon-germanium (SiGe), and the active layers ACL may be formed of orinclude silicon (Si). A germanium concentration of each of thesacrificial layers SAL may range from 10 at% to 30 at%.

Mask patterns may be respectively formed on the PMOSFET region PR andthe NMOSFET region NR of the substrate 100. The mask pattern may be aline- or bar-shaped pattern extending in a second direction D2.

A first patterning process, in which the mask patterns are used as anetch mask, may be performed to form a first trench TR1 defining a firstactive pattern AP1 and a second active pattern AP2. The first activepattern AP1 and the second active pattern AP2 may be formed on thePMOSFET region PR and the NMOSFET region NR, respectively. Each of thefirst and second active patterns AP1 and AP2 may include the sacrificiallayers SAL and the active layers ACL, which are alternately stacked inan upper portion thereof.

A second patterning process may be performed on the substrate 100 toform a second trench TR2 defining the PMOSFET region PR and the NMOSFETregion NR. The second trench TR2 may be formed to be deeper than thefirst trench TR1.

A device isolation layer ST may be formed on the substrate 100 to fillthe first and second trenches TR1 and TR2. For example, an insulatinglayer may be formed on the substrate 100 to cover the first and secondactive patterns AP1 and AP2. The device isolation layer ST may be formedby recessing the insulating layer until the sacrificial layers SAL areexposed.

The device isolation layer ST may be formed of or include an insulatingmaterial (e.g., silicon oxide). Each of the first and second activepatterns AP1 and AP2 may include an upper portion protruding above thedevice isolation layer ST. For example, the upper portion of each of thefirst and second active patterns AP1 and AP2 may vertically protrudeabove the device isolation layer ST.

Referring to FIGS. 5A and 5B, sacrificial patterns PP may be formed onthe substrate 100 to cross the first and second active patterns AP1 andAP2. Each of the sacrificial patterns PP may be formed to have a line-or bar-shape extending in the first direction D1. The sacrificialpatterns PP may be arranged, with a specific pitch, in the seconddirection D2.

In detail, the formation of the sacrificial patterns PP may includeforming a sacrificial layer on the substrate 100, forming hard maskpatterns MP on the sacrificial layer, and patterning the sacrificiallayer using the hard mask patterns MP as an etch mask. The sacrificiallayer may be formed of or include poly silicon.

A pair of gate spacers GS may be formed on opposite side surfaces ofeach of the sacrificial patterns PP. The formation of the gate spacersGS may include conformally forming a gate spacer layer on the substrate100 and anisotropically etching the gate spacer layer. The gate spacerlayer may be formed of or include at least one of SiCN, SiCON, or SiN.Alternatively, the gate spacer layer may be a multi-layered structureincluding at least two of SiCN, SiCON, or SiN.

Referring to FIGS. 6A to 6D, first recesses RS1 may be formed in upperportions of the first active pattern AP1. The second recesses RS2 may beformed in upper portions of the second active pattern AP2. During theformation of the first and second recesses RS1 and RS2, the deviceisolation layer ST may be recessed at both sides of each of the firstand second active patterns AP1 and AP2 (e.g., see FIG. 6C).

In detail, the first recesses RS1 may be formed by etching upperportions of the first active pattern AP1 using hard mask patterns MA andthe gate spacers GS as an etch mask. Each of the first recesses RS1 maybe formed between each pair of the sacrificial patterns PP. The secondrecesses RS2 in the upper portion of the second active pattern AP2 maybe formed by the same method as that for the first recesses RS1.

Referring to FIGS. 7A to 7D, first source/drain patterns SD1 may beformed in the first recesses RS1, respectively. Specifically, a firstSEG process, in which an inner surface of the first recess RS1 is usedas a seed layer, may be performed to form a first semiconductor layerSEL1. The first semiconductor layer SEL1 may be grown as first to thirdsemiconductor patterns SP1, SP2, and SP3 and the substrate 100, whichare exposed through the first recess RS1, as a seed. As an example, thefirst SEG process may include a chemical vapor deposition (CVD) processor a molecular beam epitaxy (MBE) process.

The first semiconductor layer SEL1 may be formed of or include asemiconductor material (e.g., SiGe) having a lattice constant greaterthan that of the substrate 100. The first semiconductor layer SEL1 maybe formed to have a relatively low germanium concentration. In otherexample embodiments, the first semiconductor layer SEL1 may be providedto contain only silicon (Si) and not germanium (Ge). The germaniumconcentration of the first semiconductor layer SEL1 may range from 0 at%to 10 at%.

A second semiconductor layer SEL2 may be formed by performing a secondSEG process on the first semiconductor layer SEL1. The secondsemiconductor layer SEL2 may be formed to completely fill the firstrecess RS1. The second semiconductor layer SEL2 may be provided to havea relatively high germanium concentration. As an example, the germaniumconcentration of the second semiconductor layer SEL2 may range from 30at% to 70 at%.

The first and second semiconductor layers SEL1 and SEL2 may constitutethe first source/drain pattern SD1. The first and second semiconductorlayers SEL1 and SEL2 maybe doped with impurities in situ during thefirst and second SEG processes. Alternatively, the first source/drainpattern SD1 may be doped with impurities, after the formation of thefirst source/drain pattern SD1. The first source/drain pattern SD1 maybe doped to have a first conductivity type (e.g., p-type).

Second source/drain patterns SD2 may be formed in the second recessesRS2, respectively. Specifically, the second source/drain pattern SD2 maybe formed by a SEG process using an inner surface of the second recessRS2 as a seed layer. In example embodiments, the second source/drainpattern SD2 may be formed of or include the same semiconductor material(e.g., Si) as the substrate 100. The second source/drain pattern SD2 maybe doped to have a second conductivity type (e.g., n-type). The innerspacers IP may be respectively formed between the second source/drainpattern SD2 and the sacrificial layers SAL. The formation of the innerspacers IP and the second source/drain pattern SD2 will be described inmore detail with reference to FIGS. 11 to 19 .

Referring to FIGS. 8A to 8D, a first interlayer insulating layer 110 maybe formed to cover the first and second source/drain patterns SD1 andSD2, the hard mask patterns MP, and the gate spacers GS. As an example,the first interlayer insulating layer 110 may include a silicon oxidelayer.

The first interlayer insulating layer 110 may be planarized to exposetop surfaces of the sacrificial patterns PP. The planarization of thefirst interlayer insulating layer 110 may be performed using anetch-back or chemical-mechanical polishing (CMP) process. All of thehard mask patterns MP may be removed during the planarization process.As a result, a top surface of the first interlayer insulating layer 110may be coplanar with the top surfaces of the sacrificial patterns SAPand the top surfaces of the gate spacers GS.

In example embodiments, the exposed sacrificial patterns PP may beselectively removed. As a result of the removal of the sacrificialpattern PP, first empty spaces ET1 may be formed to expose the first andsecond active patterns AP1 and AP2 (e.g., see FIG. 8D).

In example embodiments, some of the sacrificial patterns PP may not beremoved. For example, the sacrificial pattern PP on the cell boundarymay not be removed. Specifically, a mask layer may be formed on some ofthe sacrificial patterns PP, which should not be removed, to reduce orprevent them from being removed by the selective removal process of thesacrificial patterns PP. As a result of the removal of the sacrificialpattern PP, the first and second active patterns AP1 and AP2 may beexposed through the first empty space ET1. The sacrificial layers SAL ofeach of the first and second active patterns AP1 and AP2 may be exposedthrough the first empty space ET1.

Referring to FIGS. 9A to 9D, the sacrificial layers SAL, which areexposed through the first empty space ET1, may be selectively removed.In detail, an etching process may be performed in such a way that onlythe sacrificial layers SAL are selectively removed without etching ofthe first to third semiconductor patterns SP1, SP2, and SP3.

The etching process may be chosen to exhibit a high etch rate for amaterial (e.g., SiGe) having a relatively high germanium concentration.For example, the etching process may have a high etch rate forsilicon-germanium whose germanium concentration is higher than 10 at%.

During the etching process, the sacrificial layers SAL may be removedfrom the PMOSFET region PR and the NMOSFET region NR. The etchingprocess may be a wet etching process. An etching material, which is usedin the etching process, may be chosen to quicklsy remove the sacrificiallayer SAL having a relatively high germanium concentration. Meanwhile,during the etching process, the first source/drain pattern SD1 in thePMOSFET region PR may be protected by the first semiconductor layer SEL1having a relatively low germanium concentration.

Referring back to FIG. 9D, since the sacrificial layers SAL areselectively removed, only the first to third semiconductor patterns SP1,SP2, and SP3 may be left on each of the first and second active patternsAP1 and AP2. That is, second empty spaces ET2 may be formed as a resultof the removal of the sacrificial layers SAL. The second empty spacesET2 may be formed between the first to third semiconductor patterns SP1,SP2, and SP3.

Referring to FIGS. 10A to 10D, a gate insulating layer GI may beconformally formed in the first and second empty spaces ET1 and ET2. Agate electrode GE may be formed on the gate insulating layer GI. Thegate electrode GE may be formed to fill the first and second emptyspaces ET1 and ET2. Specifically, the gate electrode GE may includefirst to third portions PO1, PO2, and PO3 filling the second emptyspaces ET2. The gate electrode GE may further include a fourth portionPO4 filling the first empty space ET1. A gate capping pattern GP may beformed on the gate electrode GE.

Referring back to FIGS. 1 and 2A to 2D, a second interlayer insulatinglayer 120 may be formed on the first interlayer insulating layer 110.The second interlayer insulating layer 120 may include a silicon oxidelayer. Active contacts AC may be formed to penetrate the secondinterlayer insulating layer 120 and the first interlayer insulatinglayer 110 and to be electrically connected to the first and secondsource/drain patterns SD1 and SD2. A gate contact GC may be formed topenetrate the second interlayer insulating layer 120 and the gatecapping pattern GP and to be electrically connected to the gateelectrode GE.

A pair of division structures DB may be formed at both sides of a logiccell LC. The division structure DB may be formed to penetrate the secondinterlayer insulating layer 120, a remaining portion of the sacrificialpattern PP, and an upper portion of the active pattern AP1 or AP2 belowthe sacrificial pattern PP. The division structure DB may be formed ofor include at least one of insulating materials (e.g., silicon oxide orsilicon nitride).

A third interlayer insulating layer 130 may be formed on the activecontacts AC and the gate contacts GC. A first metal layer M1 may beformed in the third interlayer insulating layer 130. A fourth interlayerinsulating layer 140 may be formed on the third interlayer insulatinglayer 130. A second metal layer M2 may be formed in the fourthinterlayer insulating layer 140.

The formation of the inner spacers IP and the second source/drainpattern SD2 will be described in more detail with reference to FIGS. 11to 19 . Referring to FIG. 11 , the second recess RS2 may be formedbetween a pair of the sacrificial patterns PP. The second recess RS2 inthe second direction D2 may have a width increasing in the thirddirection D3. The first to third semiconductor patterns SP1, SP2, andSP3 and the substrate 100 may be exposed through the second recess RS2.The sacrificial layers SAL may be exposed through the second recess RS2.

Referring to FIG. 12 , the exposed sacrificial layers SAL may beselectively etched by an isotropic etching process. Specifically, theexposed sacrificial layers SAL may be recessed by a wet etching processthrough the second recess RS2. As a result of the recess of thesacrificial layers SAL, third recesses RS3 may be formed. Each of thethird recesses RS3 may be a region that is horizontally recessed in adirection away from the second recess RS2. As an example, since thethird recess RS3 is formed, at least one of the sacrificial layers SALmay be formed to have the recessed side surface RSW.

Referring to FIG. 13 , an inner insulating layer ISL may be conformallyformed in the second and third recesses RS2 and RS3. The innerinsulating layer ISL may be formed to just partially fill the thirdrecess RS3. In other words, the inner insulating layer ISL may have athickness T1 that is less than half of a height H1 of the third recessRS3 in the third direction D3 (e.g., T1 < H½). For example, the innerinsulating layer ISL may be formed of or include at least one of siliconoxide or low-k dielectric materials whose dielectric constants are lowerthan that of silicon oxide.

Referring to FIG. 14 , a protection layer PTL may be formed to fullyfill the third recesses RS3 covered with the inner insulating layer ISL.The protection layer PTL may be formed of or include at least one ofmaterials having an etch selectivity with respect to the innerinsulating layer ISL. For example, the protection layer PTL may beformed of or include at least one of aluminum oxide or silicon oxide.

Referring to FIG. 15 , an isotropic etching process may be performed toselectively etch the protection layer PTL. The etching process may beperformed to expose the inner insulating layer ISL on the first to thirdsemiconductor patterns SP1, SP2, and SP3. For example, the protectionlayer PTL may be etched to expose portions of the inner insulating layerISL covering side surfaces of the first to third semiconductor patternsSP1, SP2, and SP3.

Referring to FIG. 16 , the portions of the inner insulating layer ISL,which are exposed by the etching of the protection layer PTL, may beetched. For example, the exposed portions of the inner insulating layerISL may be removed by the etching step, and thus, inner insulatingpatterns ISP may be localized in the third recesses RS3, respectively.As the removal of the exposed portions of the inner insulating layerISL, the first to third semiconductor patterns SP1, SP2, and SP3 and thesubstrate 100 may again be exposed again through the second recess RS2.

Referring to FIG. 17 , the remaining portion of the protection layer PTLmay be completely removed. The removal of the protection layer PTL maybe performed in the same or substantially the same manner as that in theafore-described process of selectively etching the protection layer PTL.Since the protection layer PTL is completely removed, only the innerinsulating pattern ISP may be left in the third recess RS3. Theremaining space of the third recess RS3 other than the inner insulatingpattern ISP may be an empty space.

Referring to FIG. 18 , an epitaxial layer EPL may be formed by a SEGprocess, in which the first to third semiconductor patterns SP1, SP2,and SP3 and the substrate 100 exposed through the second recess RS2 areused as a seed layer. The epitaxial layer EPL may not be grown on theinner insulating pattern ISP.

The epitaxial layer EPL may be grown with a specific directionality. Theepitaxial layer EPL may be mainly grown in a direction toward the centerof the second recess RS2. In other words, a growth speed of theepitaxial layer EPL may be fastest in a direction toward the center ofthe second recess RS2. Due to the inner insulating pattern ISP, theepitaxial layer EPL may be reduced or prevented to be grown in the thirdrecess RS3. Thus, the epitaxial layer EPL may be grown to mainly fillthe second recess RS2, but not the third recess RS3.

Referring to FIG. 19 , since the epitaxial layer EPL is formed to fillthe second recess RS2, the second source/drain pattern SD2 may be formedin the second recess RS2. Specifically, the epitaxial layers EPL, whichare respectively grown from the first to third semiconductor patternsSP1, SP2, and SP3 and the substrate 100, may be merged to form each ofthe second source/drain patterns SD2.

Due to the directionality in the growth of the epitaxial layer EPL, thesecond source/drain pattern SD2 may be formed to fill the second recessRS2, but not the third recess RS3. Thus, a remaining space of the thirdrecess RS3, which is not filled with the second source/drain patternSD2, may be defined as the air gap AG. Since the inner spacer IPincludes the inner insulating pattern ISP, which is formed of a low-kdielectric material, and the air gap AG, the inner spacer IP may beformed to have a dielectric constant close to that of the air.

The inner insulating pattern ISP and the air gap AG in the third recessRS3 may constitute the inner spacer IP. The sacrificial layer SAL may bespaced apart from the second source/drain pattern SD2 by the innerspacer IP.

FIGS. 20 to 22 are enlarged sectional views, each of which is providedto described a semiconductor device according to example embodiments ofthe inventive concepts and to illustrate the portion M of FIG. 2B. Inthe following description, an element previously described withreference to FIGS. 1, 2A to 2D, and 3 may be identified by the samereference number without repeating an overlapping description thereof,for the sake of brevity.

Referring to FIG. 20 , the air gap AG may include a gap region AGR and aprotruding region AGP, which is extended from the gap region AGR towardthe second source/drain pattern SD2. The gap region AGR may be enclosedby the inner insulating pattern ISP. The protruding region AGP may beenclosed by the second source/drain pattern SD2.

Specifically, a second air gap AG2 will be described exemplarily. Thegap region AGR of the second air gap AG2 may have a second height H2 inthe third direction D3. The protruding region AGP of the second air gapAG2 may have a third height H3 in the third direction D3. The thirdheight H3 may be decreased with increasing distance from the gap regionAGR. The largest value of the third height H3 may be larger than thesecond height H2. Accordingly, the second air gap AG2 may have an arrowshape. A first side surface OSW1 of the second source/drain pattern SD2may have a concave profile, which corresponds to the protruding shape ofthe protruding region AGP.

Referring to FIG. 21 , the air gap AG may include the gap region AGR andthe protruding region AGP. Specifically, the second air gap AG2 will bedescribed exemplarily. The gap region AGR of the second air gap AG2 mayhave a second height H2. The protruding region AGP of the second air gapAG2 may have a fourth height H4. The fourth height H4 may be decreasedwith increasing distance from the gap region AGR. However, unlike thestructure of FIG. 20 , the largest value of the fourth height H4 may beequal to or smaller than the second height H2. Accordingly, the secondair gap AG2 may have a pentagonal shape.

Referring to FIG. 22 , the second source/drain pattern SD2 may include aprotruding pattern SDP extended into the air gap AG. The protrudingpattern SDP may be extended into the air gap AG but may not fill theentire inner space of the air gap AG.

Specifically, the second air gap AG2 will be described exemplarily. Thesecond air gap AG2 may have a second height H2. The protruding patternSDP may have a fifth height H5 in the third direction D3. The fifthheight H5 may be decreased with increasing distance from the secondsource/drain pattern SD2. The largest value of the fifth height H5 maybe equal to or smaller than the second height H2. The second air gap AG2may have a crown shape.

Unlike the structure of FIG. 3 , a width of a first air gap AG1 may bedecreased in the third direction D3 until it reaches its smallest valueand then may be increased. Specifically, the second width W2 of thefirst air gap AG1 may be smaller than the first width W1. The secondwidth W2 of the first air gap AG1 may be smaller than the third widthW3.

The air gap AG according to example embodiments of the inventiveconcepts may have various shapes, as previously described with referenceto FIGS. 3 and 20 to 22 . The shape of the air gap AG may depend on athickness of the inner insulating pattern ISP and a process condition ofthe SEG process previously described with reference to FIG. 18 .Specifically, a growth direction of the epitaxial layer EPL of FIG. 18may be changed depending on the process condition of the SEG process,and thus, the shape of the air gap AG may be variously changed.

FIG. 23 is a sectional view, which is taken along the line A-A′ of FIG.1 to illustrate a semiconductor device according to example embodimentsof the inventive concepts. In the following description, an elementpreviously described with reference to FIGS. 1, 2A to 2D, and 3 may beidentified by the same reference number without repeating an overlappingdescription thereof, for the sake of brevity.

Referring to FIG. 23 , the inner spacers IP may also be provided on thePMOSFET region PR, like the NMOSFET region NR. In other words, the innerspacers IP may be respectively interposed between the first to thirdportions PO1, PO2, and PO3 of the gate electrode GE and the firstsource/drain pattern SD1. Each of the inner spacers IP on the PMOSFETregion PR may include the inner insulating pattern ISP and the air gapAG, like that on the NMOSFET region NR.

The inner spacers IP on the PMOSFET region PR may reduce a parasiticcapacitance between the gate electrode GE and the first source/drainpattern SD1. Thus, it may be possible to improve performance andelectric characteristics of the semiconductor device in both of theNMOSFET and PMOSFET regions NR and PR.

In example embodiments where a SEG process is used to grown a SiGelayer, defects may be easily formed on the SiGe layer, which is formedon an insulating layer, such as a silicon nitride layer or a siliconoxide layer. Thus, if the inner spacer IP is composed of only theinsulating layer, defects may be formed in the first source/drainpattern SD1, because the first source/drain pattern SD1 is formed bygrowing a SiGe layer using a SEG process. However, according to exampleembodiments of the inventive concepts, since the inner spacer IP ismainly composed of the air gap AG, it may be possible to reduce orprevent the defects from being formed during the growth process of theSiGe layer. Thus, according to example embodiments of the inventiveconcepts, it may be possible to reduce or prevent defects from beingformed in the first source/drain pattern SD1 and thereby to reduce orprevent deterioration in performance of the semiconductor device.

According to example embodiments of the inventive concepts, asemiconductor device may include an inner spacer, which is providedbetween a gate electrode and a second source/drain pattern and has avery low dielectric constant. Thus, it may be possible to reduce aparasitic capacitance between the gate electrode and the secondsource/drain pattern and to improve performance and electriccharacteristics of the semiconductor device.

While example embodiments of the inventive concepts have beenparticularly shown and described, it will be understood by one ofordinary skill in the art that variations in form and detail may be madetherein without departing from the spirit and scope of the attachedclaims.

1. (canceled)
 2. A method of fabricating a semiconductor device,comprising: forming an active pattern on a substrate; forming a stackedstructure on the active pattern, the stacked structure includingsacrificial layers and active layers that are alternately stacked on theactive pattern; forming a sacrificial pattern on the stacked structure;etching the stacked structure using the sacrificial pattern as an etchmask to form a recess in the stacked structure; etching the sacrificiallayers exposed by the recess to form indented regions, respectively;forming an inner insulating layer in the indented regions, the innerinsulating layer partially fill the indented regions; forming aprotection layer on the inner insulating layer to fill the indentedregions; removing portions of the inner insulating layer covering theactive layers using the protection layer as an etch mask, the remaininginner insulating layer forms inner insulating patterns separated fromeach other; removing the protection layer; and forming a source/drainpattern in the recess, wherein air gaps are formed between thesource/drain pattern and the inner insulating patterns as a result ofthe removing of the protection layer.
 3. The method of claim 2, furthercomprising replacing the sacrificial pattern and the sacrificial layerswith a gate electrode, wherein the gate electrode includes innerelectrodes corresponding to the sacrificial layers, respectively.
 4. Themethod of claim 2, wherein the inner insulating layer comprises siliconoxide or a material whose dielectric constant is lower than siliconoxide.
 5. The method of claim 2, wherein the air gaps are formed in theindented regions, respectively, wherein the air gaps include a first airgap and a second air gap located higher than the first air gap.
 6. Themethod of claim 5, wherein a volume of the first air gap is larger thana volume of the second air gap.
 7. The method of claim 2, wherein one ofthe air gaps includes a gap region and a protruding region, theprotruding region extending toward the source/drain pattern, theprotruding region having a first height in a direction perpendicular toa top surface of the substrate, the gap region having a second height inthe direction perpendicular to the top surface of the substrate, and alargest value of the first height being larger than a largest value ofthe second height.
 8. The method of claim 2, wherein the source/drainpattern includes a protruding pattern extending into one of the airgaps.
 9. The method of claim 2, wherein a bottom surface of thesource/drain pattern is in contact with the active pattern, and whereinthe source/drain pattern has a conductivity of an n-type.
 10. The methodof claim 2, wherein forming the source/drain pattern comprises formingan epitaxial layer on the active layers by performing a selectiveepitaxial growth process.
 11. The method of claim 2, further comprisingetching the protection layer by an isotropic etching process to exposethe portions of the inner insulating layer.
 12. A method of fabricatinga semiconductor device, comprising: forming an active pattern on asubstrate; forming a source/drain pattern on the active pattern; forminga channel pattern connected to the source/drain pattern, the channelpattern comprising semiconductor patterns that are stacked and spacedapart from each other; forming a gate electrode on the channel pattern,the gate electrode comprising an inner electrode between the activepattern and a lowermost one of the semiconductor patterns; and formingan inner spacer between the inner electrode and the source/drainpattern, wherein the forming of the inner spacer comprises: forming anindented region in a recess where the source/drain pattern is formed;forming an inner insulating layer in the indented region; forming aprotection layer on the inner insulating layer to fill the indentedregion; and forming an air gap by removing the protection layer.
 13. Themethod of claim 12, wherein the inner insulating layer comprises siliconoxide or a material whose dielectric constant is lower than siliconoxide.
 14. The method of claim 12, wherein the forming of the innerspacer further comprises: etching the protection layer by an isotropicetching process to expose a portion of the inner insulating layer; andremoving the portion of the inner insulating layer using the protectionlayer as an etch mask.
 15. The method of claim 12, wherein the air gapincludes a gap region and a protruding region, the protruding regionextending toward the source/drain pattern, the protruding region havinga first height in a direction perpendicular to a top surface of thesubstrate, the gap region having a second height in the directionperpendicular to the top surface of the substrate, and a largest valueof the first height being larger than a largest value of the secondheight.
 16. The method of claim 12, wherein the source/drain patternincludes a protruding pattern extending into the air gap.
 17. A methodof fabricating a semiconductor device, comprising: forming a firstactive pattern and a second active pattern on PMOSFET and NMOSFETregions of the substrate, respectively; forming a first active patternand a second active pattern on the PMOSFET and NMOSFET regions,respectively; forming a first source/drain pattern and a secondsource/drain pattern on the first active pattern and the second activepattern, respectively; forming a first channel pattern and a secondchannel pattern, connected to the first source/drain pattern and thesecond source/drain pattern, respectively, and each of which includes afirst semiconductor pattern, a second semiconductor pattern, and a thirdsemiconductor pattern sequentially stacked to be spaced apart from eachother; forming a first gate electrode and a second gate electrode on thefirst and second channel patterns, respectively, each of the first andsecond gate electrodes comprising a first inner electrode between thesubstrate and the first semiconductor pattern, a second inner electrodebetween the first semiconductor pattern and the second semiconductorpattern, a third inner electrode between the second semiconductorpattern and the third semiconductor pattern, and an outer electrode onthe third semiconductor pattern; forming inner spacers, between thefirst to third inner electrodes and the second source/drain pattern;forming a first gate insulating layer and a second gate insulatinglayer, between the first channel pattern and the first gate electrodeand between the second channel pattern and the second gate electrode,respectively; forming a first gate spacer and a second gate spacer onside surfaces of the first and second gate electrodes, respectively;forming a first gate capping pattern and a second gate capping patternon top surfaces of the first and second gate electrodes, respectively;forming active contacts coupled to the first and second source/drainpatterns, respectively; forming gate contacts coupled to the first andsecond gate electrodes, respectively; and forming a metal layercomprising first interconnection lines that are electrically connectedto the active contacts and the gate contacts, wherein the forming of theinner spacers comprises: forming indented regions in a recess where thesecond source/drain pattern is formed; forming an inner insulating layerin the indented regions; forming a protection layer on the innerinsulating layer to fill the indented regions; and forming air gaps inthe indented regions by removing the protection layer.
 18. The method ofclaim 17, wherein the inner insulating layer comprises silicon oxide ora material whose dielectric constant is lower than silicon oxide. 19.The method of claim 17, wherein the forming of the inner spacer furthercomprises: etching the protection layer by an isotropic etching processto expose a portion of the inner insulating layer; and removing theportion of the inner insulating layer using the protection layer as anetch mask.
 20. The method of claim 17, one of the air gaps includes agap region and a protruding region, the protruding region extendingtoward the source/drain pattern, the protruding region having a firstheight in a direction perpendicular to a top surface of the substrate,the gap region having a second height in the direction perpendicular tothe top surface of the substrate, and a largest value of the firstheight being larger than a largest value of the second height.
 21. Themethod of claim 17, wherein the second source/drain pattern includes aprotruding pattern extending into one of the air gaps.